text:
What's the differences and the risk of duplicates, between ADS-B and TIS-B addresses? (inc. ICAO and self-assigned options)
What is:

ADS-B ICAO addresses
TIS-B ICAO addresses
ADS-B self-assigned addresses
TIS-B track file id

How likely is a name collision between the self-assigned address and track file id?
How likely is a name collision between the two gld90 ICAO addresses?
How likely is a name collision between the two ADS-B addresses?
How likely is a name collision between the two TIS-B addresses?
Can you give me examples of the four types?

I think you are correct. I'm processing GLD90 traffic packets and trying to understand the packet. The GLD90 protocol has separate address types for those four things listed.

Direct answers to your questions

What are ADS-B ICAO addresses  What GLD 90 calls "ICAO addresses", are the permanent addresses assigned by registries from ICAO blocks. See sections ICAO 24-bit address overall and Permanent addresses.

What are ADS-B self-assigned addresses  The anonymous addresses used only on UAT channel. See section Anonymous address (for UAT only)

What are TIS-B addresses  They are permanent ICAO addresses already mentioned. Permanent addresses are used both by ADS-B and TIS-B.

What are TIS-B trackfile ID  The 12 random bits assigned to tracks by a ground radars for Mode A/C targets which don't use Mode S (thus don't disclose a 24-bit address). These bits are added to the 12 bits of the squawk code to build a pseudo Mode S address which can be used in TIS-B messages. See TIS-B pseudo-address section.

Collision between the two GLD 90 ICAO addresses.  Permanent addresses are unique for aircraft but can collide because of errors when configuring the equipment. In addition ground vehicles are allowed to share the same permanent address when they are distant by more than 1,000km. See section Duplicates.

Collision between addresses of all kinds  See section Duplicates, as it cannot be summarized here.

Examples of the four types  permanent ICAO addresses are part of blocks allocated to a State registry, and not all blocks are currently allocated. Uruguay is allocated the block of addresses starting with 0xE90 (1110 10 010 000), so 0xE90AAA (1110 10 010 000 1010 1010 1010) is a permanent address for an aircraft registered in Uruguay.
For the other types, any valid 24-bit combination can be found as they are random. Nothing distinguishes them.

I'm adding detailed explanations below. Most of the information comes from ICAO Annex 10 volume III - Communication Systems.

ICAO 24-bit address overall

Aircraft, aerodrome vehicles, surface obstacles and Mode S surface equipments used for surveillance and radar monitoring can be assigned an address.

An aircraft is assigned a unique address. Surface vehicles and devices can share the same address, provided they are distant by more than 1,000km.

The address is assigned e.g. to the aircraft. It is not assigned to a particular equipment, all equipments aboard the aircraft use the same ICAO address (1090 ES and 978 UAT).

Valid addresses are all combinations of 24 bits, excluding all 0s and all 1s.

TIS-B pseudo-address
Addresses mentioned above are used by aircraft working with Mode S. In particular ADS-B periodic messages allow aircraft to track other aircraft positions in real time. This excludes aircraft in Mode A/C from the tracking. TIS-B is used to fill the gap.
The ground station tracking the Mode A/C aircraft sends TIS-B position reports to Mode S aircraft, related to the Mode A/C aircraft.
But in Mode S all aircraft are identified by their ICAO address, not by their Mode A/C squawk code. The ground station must temporarily identify the Mode A/C aircraft with a pseudo-address made of the 12 bits of the squawk code and 12 random bits assigned to the track.
See this question for details (with a bit of luck, @DeltaLima will post an answer here, he's a specialist in this field)
Permanent address
A permanent address is assigned by the State registry. This is a two-step process:

Address blocks are allocated by ICAO to State registries, per table 9.1 in Annex 10.

The State registry then assigns addresses to aircraft by picking in its allocated block.

Special blocks are allocated to ICAO and not available to State registries.

1000-10-011-001-00 (1000-address block)
1111-00-001-001-00 (1000-address block)
1111-00-000 (32,000-address block)

Temporary address
ICAO block 1111-00-001-001-00 is used for temporary addresses, when users are waiting for the registering procedure to complete. Assignment is administered by ICAO, not by a State registry.
Anonymous address (for UAT only)
For privacy purposes, a pseudo-random self-assigned address can be built by the aircraft equipment, starting from the permanent address if there is one, else from the current time, see this question for details.
Duplicates
The probability to see the same address in a given area is very low, but not null, because:

The same permanent address can be re-used by surface equipments distant by more than 1,000km.

Errors can be made while configuring the permanent address in the equipment (some questions on the site relate to flight trackers identifying the wrong aircraft due to address configuration mistakes).

Self-assigned UAT addresses conflicting either with a permanent address or another self-assigned address. The probability is lower than the one of a permanent address duplicate.

Perhaps the same for self-assigned TIS-B target addresses.

GDL 90
All address types can be found in field 'aa aa aa' of a GDL 90 message. The uniqueness of this field, even combined with field 't' cannot be guaranteed. How addresses call collide has been explained in section Duplicates

t=0 is any normal aircraft emitting ads-b?
t=2 is any normal aircraft emitting tis-b?
t=1 is what?
t=3 is what?

any chance you could reframe the answer around the specific address types I listed? ie t=0 through to t=4.

@codeMetis: This is a bit remote from the current question focused on address assignment. You should post another question, focused on GDL 90 fields. Whatever, messages can be ADS-B or TIS-B and the address used can be from a registry (ICAO) or self-assigned according to the principles described in the answer, thus types 0-3. See §3.5.1.2. Types 4 and 5 identify a surface equipment regardless of the datalink used. I've updated the answer to explain what are TIS-B target addresses.

my apologies, I meant to ask about the 4 specific kinds of address types that I listed in my question. Sorry if that wasn't clear.

@codeMetis. All your previous questions were already answered, I answered the new trackfile ID question. I also added a summary at the beginning to link the explanations to your questions.


text:
In gld90 protocol what is t=0-4 in a traffic report message
In gld90 protocol what is t=0-4 in a traffic report message:

t=0: ADS-B ICAO addresses
t=1: TIS-B ICAO addresses
t=2: ADS-B self-assigned addresses
t=3: TIS-B track file id

How likely is a name collision between the self-assigned address and track file id?
How likely is a name collision between the two gld90 ICAO addresses?
How likely is a name collision between the two ADS-B addresses?
How likely is a name collision between the two TIS-B addresses?
Can you give me examples of the four types?

As far as I understand, all these questions have been answered in What's the differences and the risk of duplicates, between ADS-B and TIS-B addresses? (inc. ICAO and self-assigned options)

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sort: votes


text:
What is the difference between autopilot and autoflight?
Can you please give me some explanations about autopilot and autoflight system?

Why did two people think it was a good idea to welcome a new user with a downvote, without explaining why they disliked a reasonable question. It may not have been written in the best form, but please not that not everybody here speak english as their first language.

Autoflight is the general term describing all of the following:

Flight Director: A guidance system for the pilot and autopilot with various modes. See What is a "Flight Director"? for details.
Autopilot: A system controlling the flight control surfaces to follow the flight director.
Autothrottle / Autothrust: A system setting engine thrust automatically depending on the selected mode. See also What is Auto-thrust?.

For example, the Boeing 737 NG FCOM describes it as follows (Vol. 2, Chapter 4 - Automatic Flight):

The automatic flight system (AFS) consists of the autopilot flight director system
  (AFDS) and the autothrottle (A/T). The flight management computer (FMC)
  provides N1 limits and target N1 for the A/T and command airspeeds for the A/T
  and AFDS.
The AFDS and A/T are controlled using the AFDS mode control panel (MCP) and
  the FMC. Normally, the AFDS and A/T are controlled automatically by the FMC
  to fly an optimized lateral and vertical flight path through climb, cruise and
  descent.
AFS mode status is displayed on the flight mode annunciation on each pilot’s
  primary display.

Related: What is the relationship between "automatic flight control system AFCS", "autopilot", "flight director" and "flight management system FMS"?

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text:
Flying Considerations during an Eclipse?
August 21, 2017 will see a total eclipse of the sun across large sections of the United States, generally between about 10a.m. and 2p.m. (depending on location and timezone)
If one is flying during the eclipse, are there considerations, other than sudden transitions to darkness and then to light, that should be taken into account?
Do Pilots flying during this time need to be Night Current?
Can time logged during the eclipse be logged as Night Conditions?

Good point; I edited the question to ask about other considerations such as temperatures and winds.

Related

@kevin The other question is about the UK, this one is US

@Pondlife that's true but the accepted answer provides the US regulations as well.

@fooot Yes, I'm just not a fan of "that other question has the answer even though it's actually a different question". In this case it's probably reasonable enough (the other question does mention the US, although it's secondary) but it's the principle of the thing. Maybe I'm overthinking it :-)

Hmm... In its current state, this does not seem like a duplicate to me. The answer to the other question answers part of this question, but not all of it. Similarly, there's information that would be relevant here that would not answer the other question (temperature, wind, etc.)

Do Pilots flying during this time need to be Night Current?

No, that time does not fall within what the FAA considers "night"
The FAA defines night currency in FAA FAR 61.57

FAA FAR 61.57
(b) Night takeoff and landing experience. (1) Except as provided in
  paragraph (e) of this section, no person may act as pilot in command
  of an aircraft carrying passengers during the period beginning 1
  hour after sunset and ending 1 hour before sunrise, unless within
  the preceding 90 days that person has made at least three takeoffs and
  three landings to a full stop during the period beginning 1 hour after
  sunset and ending 1 hour before sunrise, and—

Can time logged during the eclipse be logged as Night Conditions?

Nope, same reason as above it does not fall in what the FAA considers "night".

So if the Sun were to suddenly disappear during the day, then despite being in eternal night, the FAA would call it "day" because the sun never set? :D

@NickT I guarantee you that, if that ever happens, FAA regulations will be the least weird thing going on!

To log night time, the flight needs to occur between evening civil twilight and the beginning of morning civil twilight, as published in the Air Almanac, converted to local time.  - FAR §1.1

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text:
For length in aircraft design, and in weight and balance manuals, what measurement unit does Airbus use?
What length measurement unit does Airbus use for aircraft design and in their weight and balance manuals? Meters or centimeters?
Possibly they use both like Boeing does for, say, feet plus inches for overall length and wingspan but just inches for a position along the longitudinal axis for crew, pax, and cargo locations? For example 1821.0 inches for the lower hold aftmost ULD position on a 747.

Are you asking about something specific like station numbers (for things like ribs and fuselage frames)?

@Hobbes I'm interested in the balance arms along the longitudinal axis for crew, pax, fuel and cargo locations. Station numbers typically reflect the balance arms in the first model designs but then may not when when the original design is lengthened.

Terry, do you consider meter and centimeter as two distinct units? In my view they are not. They only have an impact on the presentation of significant digits.

@bogl Even if I might like to consider them as different gradations of the same unit, practical usage forces me to treat them as distinct units. If I am presented with a number delineating the position of a ULD along the longitudinal axis of an airplane, the code I write to calculate the c.g. has to take into account whether that number is in meters or centimeters.

Structures are soft metric. Airbus uses inch hardware so some measurements make sense in inches but are drawn with an ugly mm number. The coordinate system is in metric.
The rest of the aircraft is hard metric. For example, MTOW and fuel capacity is in a nice number of kg.
Documentation and instrumentation is localized according to the operator. Mass, as in fuel, can be switched between kg and lbs on ECAM, and all the manuals and W&B will follow.
There's a few units that aren't localized, most notably pressure is always in PSI and engine oil is always given in quarts (probably since it comes in quart cans).

In the FCOM for the A320 the dimensions are listed in both decimal meters and in feet+inches.

source: A320 FCOM

I also notice that in this particular FCOM they use the point for a decimal, but in a few places above they apparently missed changing them from the comma decimal more common in France

At least they didn't specify three decimal digits; a tail width of 12,450m or 11,510m between the engine centers might have been "obviously wrong", but could still lead to a bit of headscratching in less obvious situations.

The (few) design drawings I‘ve seen were in millimeters; however I can’t confirm whether that’s the uniform standard.
I think the operations manuals are available in metric and imperial units for the operator to choose.


text:
What are the off-airfield rules for private helicopters in New Zealand?
I'm a Switzerland-based private helicopter pilot planning to spend some time in NZ. I'm wondering what are the rules there regarding off-airfield landing. Is it possible at all? Is the land owner approval required? Are their any altitude limitations like in Switzerland? What are the typical practices there?

I believe the relevant rules around helicopter landings are covered by CAA Part 91 section 91.127 Use of aerodromes.
You are permitted to land a helicopter off-airfield. Land owner approval is required (except in the case of emergency), just like any other use of land.

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text:
What is the meaning of Spirit ###?
This Popular Mechanics article writes (about the B-2 Spirit).

Only 543 people have ever flown in the cockpit of a B-2. Upon landing I'll become number 544, with the new Air Force handle "Spirit 544."

Do people who have flown in B-2 Spirits have the Air Force handle "Spirit ###?"
If so, which regulation/directive/etc. specifies that the handle of people who have ever flown in the cockpit of a B-2 Spirit be "Spirit ###?"

@downvoter, Please comment or edit the question to improve it? Thanks!

I’m not voting to close as “too broad” since it’s a very specific question, but it leans pretty far toward useless gee whiz trivia, uninteresting to nearly everyone. I suspect that explains the downvotes. But I don’t think it’s worth closing.

@RalphJ I'm sorry you feel this way. This was definitely not my intention. I will promptly remove the gee whiz trivia portion. Also, I wasn't going to use this as trivia. I was genuinely curious.

@RalphJ Is the question better now? Or would you recommend deletion?

@all Any comments are appreciated.

I think you should rephrase the question title as "What is the meaning of Sprit ###?" and edit the detail of the question to indicate you think this is and then put your 2 subquestions.

@ManuH Thanks for the advice, I will do so.

I suspect the title was meant to refer to "Spirit", not "Sprit", since the former is what you're using in the question body. If I'm wrong, feel free to roll back the edit.

@aCVn Good catch, thanks!

US military aviators get to choose their own 'handles' (callsigns), like "Maverick" and "Goose", so presumably it's a tradition that B-2 aviators choose "Spirit ###" as their handle. It doesn't have to be a regulation.

@DJClayworth As I understand it, their squadron mates choose their callsign.

That US military pilots have a handle? Yes.

Spirit XXX (Number) and Callsigns are different.
Spirit Number is the order of having flown the B-2. This Covers Pilots and VIP, journalist or having been reward with this incentive flights.
eg.
Spirit 1: July 17, 1989: B. J. Hinds, Northrop’s chief B-2 test pilot,
Spirit 2: July 17, 1989: Col. R. S. Couch "Rick" USAF First Co-pilot

This is similar to the Bandit Number used for the F-117 (and maybe the SR-71)
The current number excess 760 now.
I am sure the B-21 will have a Raider number.

Thanks for your answer! Is there actually a list of that somewhere?

I have seen no (online) public list - I assume there has to be a list and curator of it!

Ok, that's disappointing. Thanks for your answer though.

Taking your questions in order:

Do people who have flown in B-2 Spirits have the Air Force handle "Spirit ###?"

It's plausible. The author of the article says so and there doesn't seem to be any reason to lie about such a trivial detail. That said, he also refers to the pilot as "Scar" rather than as "Spirit [whatever]" so even if Spirit-number is a callsign that a pilot has earned, it doesn't mean it's necessarily the one that they'll always fly with.

If so, which regulation/directive/etc. specifies that the handle of people who have ever flown in the cockpit of a B-2 Spirit be "Spirit ###?"

There seem to be no such regulations, or if any do exist, they are applied individually. Pilot callsigns are generally given informally, according to this article, which is not an official military publication. Although the content of this article is unfortunate, it substantiates the first one. Finally, the Air Force publishes official voice call sign guidelines, which do not list regulations for pilot callsigns.

@BarryHarrison - Yes I do, but I also mean to indicate that particular group of pilots might have "rules" that are only applied within that group, such as "All our callsigns follow theme X" or "Nobody gets callsign Y in memory of pilot Y who died last year" and so on.

@BarryHarrison Sure, you could google "callsign traditions" or better, ask it as a new question here! One fairly standard rule is the bar test: your callsign will probably be embarrassing, but shouldn't be so embarrassing that you can't pick up dates at the bar with it.

I am reading this right now and part of it reads: "...one AC-130H, AF Serial No. 69-6567, call-sign Spirit 03, opted to..." So I guess Spirit isn't a unique callsign?

@BarryHarrison - At this point the comment thread is becoming an extended discussion. You should ask a new question about this new topic, so you can get more answers than just mine.


text:
Why does the main battery discharge with the alternator running?
In my cessna 172S, when engine running at any RPM, the current at the main battery is below zero, indicating that the alternator is not charging the battery or the battery discharges, but the standby battery indicates a current above zero and it is charged by the alternator.
How can this happen?

I see TAS 0kt, TIMER 00:03:29 and a slightly low OIL TEMP, so I imagine that this is soon after engine start. Is that correct? Which battery (main or standby) is the starter hooked up to? You can [Edit] your question to add clarifying information requested in comments.

I take a picture when I running up the engine for maintenance, main battery that hook up to the starter

28 is pretty high. If your machine is smart it's wise to discharge the battery a little occasionally.

Our mechanic had a similar issue with a Piper Cherokee where the battery would only charge intermittently.  It turned out there was a bad connection at the Master Switch which ran from the Alternator/voltage regulator to the Master Switch. Most of these types of electrical issues tend to be bad wiring. I would check your wiring thoroughly.

I has been perform continuity test following the wiring diagram, but the result of continuity test is ok, and this problem still exist

@AchmadSyahrulAnggaPratama Wiring can be bad in ways that still allow a simple continuity test to pass. In fact, I'd say that's probably the worst kind of bad wiring, because it would result in a voltage drop which gets dissipated as heat, and/or intermittent function. In a worst case scenario, it can even lead to arcing, which in principle can start a fire.

One of two things:  Either there is a fault somewhere between the alternator terminals and the DC aircraft electrical system and busses or you are placing a greater load on the A/C electrical system than the alternator can handle.
For electrical issues, I would have the airplane inspected by a qualified mechanic and check the alternator, the DC rectifier as well as all of the connections between these systems and the electrical busses.  For load issues, take the airplane out on the ramp where you can safely do a run-up and follow the run-up checklist for your airplane.  With the engine running at between 1700-1800 RPM, switch on all of your electrical components - all of the lights, the pitot heat, the boost pump, the 12V lighter, etc and monitor the ammeter to verify it remains positive throughout the runup.  If it starts drawing current off of the battery, you may need to have the alternator inspected and replaced.


text:
Can this aircraft be identified by the exposure pattern of its flashing lights?
Can the aircraft on the attached photo be identified from the light pattern?  While photographing this globular cluster (M 13) in Hercules, an aircraft passed through the FOV.

The width between the outer lights is 3 arc minutes and the exposure time was 15 seconds.
The photo was taken on April 23, 2019, 10:28 PM at James River State Park, Gladstone, VA.

I would be very surprised (and impressed)  if someone can 100% identify the aircraft based on this image alone. I assume you have the exact time and location so it's worth checking the history on sites like https://www.flightradar24.com

Please post the specific time and place the photo was taken.

Cool photo! You're not going to be able to identify the plane down to the model by its lights: as I recall, Boeing and Airbus have distinctively different flash patterns from each other but, without knowing the altitude of the plane, you can't tell its size, so you can't get any closer than that. (And, of course, not all planes are made by Boeing or Airbus.)

The photo was taken on April 23, 2019, 10:28 PM at James River State Park, Gladstone, VA. If we know the wingspan of the aircraft, we should be able to calculate its altitude and, perhaps, its speed from the light sequence.

The only aircraft that appears at the area (23rd April 2019 02:30 UTC) on flightradar24 is a Bombardier CRJ-200LR but I'm not convinced that it's the aircraft in the photograph as it flies at 22K ft according to fr24 but that does not match the wingspan (it should appear much smaller in the photo). So my guess will be a smaller GA aircraft that doesn't have an ADS-B transponder

@DeepSpace Wouldn't a GA plane performing an IFR flight need the transponder to be in that airspace?

@AEhere It should, but not necessarily an ADS-B capable one (which I believe is the only mode that flightradar24 and similar sites can pick up)

I find it interesting that the strobes, while sync'd are not synchronous - the left wing tip flashes before the right.

@GaryGrew can you tell us about the azimuth and elevation angle of the telescope? Given your time and location I'd expect about 88 degrees (almost east) and 34 degrees up. Can you confirm? Is there any mirroring in the image? Is "up" in the picture a higher elevation angle and left in the picture more north?

@FreeMan, the strobes are synchronous. The aircraft is seen from almost straight ahead, 28 degrees down the nose. In the view the aircraft is moving upwards and slightly to the right. Due to the celestial tracking of the telescope the traces are slightly less slanted than they would be if the telescope was static.

@GaryGrew how did you measure the width between the traces? Perpendicular to the traces or strobe to strobe (more or less horizontal). How accurate is the measurement?

No, based on the exposure pattern I can't identify the aircraft. But based on the other information you gave, I can. It's an Embraer 175, registration N287SY.

After looking up the exact position of the M13 Globular cluster at the time the photograph was taken, I found that the telescope had to be facing to 64 degrees (East-Northeast), with an elevation angle of 28 degrees.
I used in-the-sky.org to find the position of the M13 cluster.

I then drew the geodesic from  James River State Park in a heading of 64 degrees
I used academo.org to draw the geodesic on the map

Then using Flight radar 24's history/replay function I found the aircraft

The aircraft is an Embraer 175, flight DL3693,  flying at 38000 feet.
If we assume:

the telescope is at 500ft MSL,
pointing up 28 degrees above the horizon,
the atmosphere is ISA, and
the earth is flat,

then we can calculate that the aircraft would be approximately 21.5 km horizontally away.
Measuring that out on Google maps gives the following:

That measurement is perfectly in line with the flight path of the Embraer 175.
The slant distance to the aircraft is approximately 24.5 kilometres. The track angle of the aircraft is 228 degrees, so we see the aircraft almost from straight ahead.
The span is 26 meter, I assume the lights are at the wingtips (they are not). The distance between the traces is thus expected to be 3.5 arc minutes.  Close enough!

+1, Well done, mate.

This doesn't answer the question as asked, but it's so good (and probably answers the OP's real question) that I have to +1 it anyway!

All civil aircraft flying at night are required to have navigation lights and anti-collision lights.
Navigation lights comprise a red light on the left wingtip, a green light on the right wingtip, and a white light on the tail.  Each should only be visible within about 180 degrees laterally.
Anti-collision lights can be white strobes on both wingtips, a red (or white, for very old light planes) rotating or flashing beacon, or both strobes and beacon.  The beacon and/or at least one strobe should be visible from all angles.
Therefore, all planes will look roughly the same at night.  If you knew the exact altitude, you could calculate wingspan (from the distance between the navigation/strobe lights) and the ground speed (from the distance it was moving), which may imply the class of plane, but neither measure will be precise enough to distinguish a specific model or even make.

All modern Airbusses have a double-flashing strobe, most others have not, so some distinction could be possible even based on flash pattern.


text:
What is 20NM reference point in "CTC SOCAL WITHIN 20NM"?
In Los Angeles TAC you'll see magenta boxes with SOCAL frequency and other information.
I was just wondering what is 20NM reference point is? in other word, 20NM from where or what?

Possible duplicate of Why does only class C airspace have an "outer area"?

Short answer:
The primary Class C airport
Longer Answer:
Your question refers to the magenta boxes on sectional and TAC charts that read CTC SOCAL APP WITHIN 20 NM on 134.2 338.2, or equivalent:

These boxes are used in connection with the nearest Class C airspace on the chart. Arriving pilots are requested to contact approach within 20 NM of the primary Class C airport. This is the answer to your question, the primary airport of that Class C airspace. Which airspace and airport exactly will depend on which magenta boxes you look at on the Los Angeles TAC. In the chart examples above and below, that airport would be Bob Hope (KBUR).
The deeper significance behind this instruction is the procedural Outer Area of the Class C airspace which is not depicted on the charts. Though not mandatory, this outer area of the Class C airspace is still considered part of the controlled airspace, and pilots are asked to contact approach before entering this area. See section 3-2-4 of the Aeronautical Information Manual (AIM)

3-2-4 c. 2. (b)
  NOTE-
  4. Though not requiring regulatory action, Class C airspace areas have a
  procedural Outer Area. Normally this area is 20 NM from the primary
  Class C airspace airport. Its vertical limit extends from the lower
  limits of radio/radar coverage up to the ceiling of the approach
  control's delegated airspace, excluding the Class C airspace itself,
  and other airspace as appropriate. (This outer area is not charted.)

Note that the locations of the boxes on the chart (see image below) roughly correspond to the various approach sectors, with the frequencies contained in the boxes varying accordingly.
Also note that the blue boxes similarly correspond to Class B airspace, though the 20 NM note is absent, since Class B does not have the unmarked Procedural Area.

On this TAC the 20NM is not really in reference to any particular point as much as it is in reference to the "Primary Airspace" (really class B or C, which is usually referenced around an airport). So if you are within 20NM of the center (main airport) of any primary airspace, this is the frequency you could contact for flight following or to transition through the airspace. In this case, thats LAX, VNY, BUR, SNA, ONT, RIV. Boxes outlined in blue are the frequencies for entering the class B while the magenta boxes are the frequencies to contact to enter the class C (see pic below from the TAC).

These are not mandatory contact instructions outside of the airspace (although you should always check local procedures). The standard radio contact procedures apply in the given airspaces. These are printed so you don't need to pull out your AFD to look up frequencies.


text:
How do altimeters cope with varying lapse rate?
How do barometric altimeters measure altitude above atmosphere datum if the laps rate of the pressure is not uniform, not constant? Imagine these lines representing pressure lapse rate:
560hpa
570hpa
580hpa
600hpa
700hpa
800hpa
1000hpa sea level

And so on. Now imagine your plane flying through these numbers vertically, and in your kollsman windows you set the datum line 1000 so, when you get lower (in numbers) the altimeter will read higher. Now when you’re passing trough the 500hpa pressure lines you can see the lapse rate is decreasing even if your climb rate is constant. My question is, does the altimeter misread your true altitude? Does the altimeter “think” it’s lower than what it is in reality, due to lapse rate?

My impression is that over any one spot on earth the barometric pressure lapse rate is nearly constant though maybe not the same as over some other spot with different weather.  I may be wrong.

The question is unclear to me- is the plane spiralling upward over a fixed point on the ground, or flying horizontally, or what?

Yes, the altimeter will have an error to it.   All other planes in the same area with the same altimeter setting will have the same error; so you won't hit each other.  Your precise exact altitude above sea level is not relevant when you're several thousand feet up.

@abelenky: And if you're flying in IMC, you leave a good margin for error between your indicated altitude and the highest terrain (or structures) shown on your chart.

@abelenky Looks like a correct answer to me.

Yes, but it doesn't really matter.
The error that seems to be an underlying assumption in your question is that you're treating the pressure altimeter as measuring altitude. It doesn't.
Rather, it measures the difference between the static pressure and a reference pressure (the latter being the "altimeter setting").
That difference is expressed as an altitude, but it really is a difference in pressure. It could just as well be expressed as just ρref−ρstatic, the value of which would also increase as the aircraft climbs, but that would be less intuitive (and likely less precise, if not necessarily less accurate) especially when close to the ground.
(This isn't much different from how an airspeed indicator doesn't really tell you speed, it tells you the difference between static and dynamic pressure, but the scale is such that this difference in pressure is expressed as a speed. That's why the ASI acts up when the pitot tube is blocked.)
To be airworthy, an altimeter is required to display the correct value to within some margin of error which I don't know the exact value of. Vertical separation is then chosen such that the minimum difference in actual altitude, given the same altimeter setting, between two aircraft is sufficient to ensure vertical clearance between them even if both have instrument errors that are maximally unfortunate.
IMC minimum safe altitudes are also selected in a similar manner, to ensure obstacle clearance even if the altimeter is maximally out of calibration.
Since every aircraft within an area is supposed to be on the same altimeter setting, or (above the transition altitude) on the standard setting of 1013.25 hPa, as long as everyone sets their altimeter properly, the errors will all be very similar and everyone at, say, "5000 ft" or "FL310" is flying at very close to the same static pressure level, even if that level doesn't correspond exactly to 5000 ft AMSL or 31000 ft AMSL. Thus, while you're correct in theory, it is not a problem in practice.

I have a feeling that the OP's confusion is more about the fact that the atmospheric 'lapse rate' is indeed inherently non-linear. Altimeters do correct for it (mechanically or electronically) and present a linear altitude assuming standard pressure distribution. For this reason it wouldn't be correct to express it as $p_{ref}-p_{static}$, given that our aim is to provide for linear altitude separation. As for the discrepancy with 'true' (vs standard) distribution, you are right.


text:
Advances in rivet technology for Aircraft?
What advances have there been in the manufacture of rivets which are used for joining for aircraft and rivet technology and materials used?

http://www.assemblymag.com/articles/90348-aerospace-fastening-in-the-21st-century

What timeframe are you looking at?  For example, flush rivets were probably the greatest advance in history, but they're also a fairly old one.

Rivets need to be harder than the material being joined by them, and the growing use of high-strength alloys has made the use of rivets of the same material as the material being joined problematic. To set a rivet, it needs to have some plasticity, which in turn is greatly reduced when an alloy is optimized for high strength.
Initially, rivets were made from aluminium alloys, but have been replaced by fasteners, especially Hi-Loks (Hi-Lock is also used) which are (mostly) titanium or steel bolts with an aluminium or titanium nut. The nut has two parts; the lower part, the collar, has the internal thread and remains on the Hi-Lok after assembly while the upper part forms a hexagonal head for tightening with a special wrench. Between both is a groove which allows the head to shear off at the right torque. This ensures consistent torque and eliminates the need for torque inspection. The wrench needs a hex bolt at its center which serves as a socket wrench and engages with the shank of the fastener to keep it from rotating with the nut.
Why titanium? Lisi Aerospace says on its website:

By using titanium nuts rather than steel or stainless steel nuts, we
  can save up to 110kg on a single aisle aircraft and 220 kg on a wide
  body aircraft.

If access is restricted, blind fasteners are also available. Hi-Loks have been standardized and cover a wide range of sizes and shapes.

Hi-Lok fastener (picture source)
Another advance are special bolts for joining composite parts. The head of a regular fastener is too small and runs the risk of being pulled through the composite sheet. Special bolts, washers and nuts for composites spread the load out.

Composite panel fastener (picture by Alcoa Fastening systems, source)


text:
Can airlines choose whether or not to enable MCAS on their fleets, and if so, have US airlines chosen to do so?
I've been told that, although all 737 Max aircraft are equipped with MCAS, the system can be deactivated by the individual airline.  I've also heard that US airlines never activated MCAS in their 737 Max aircraft.  Any truth to either?

Where did you get that it can be deactivated by airlines? That's dubious since it's a part of the airworthiness certificate. There are optional AoA readouts and disagree warning lights. The latter of which, I believe, is planned as a mandatory retrofit for the new MCAS update.

No, MCAS was required for the 737 MAX to be certified by the FAA. It cannot be deactivated by any airline, including airlines in the U.S.

Source:

"M.C.A.S. was necessary then for the airplane [737 MAX] to be
  certified by the F.A.A. to have met all of the regulatory design
  requirements for stability and control."
https://www.nytimes.com/2019/02/03/world/asia/lion-air-plane-crash-pilots.html


text:
With an EASA PPL, can I invoice my mother's company for airplane rental to fly her to a convention, with no other renumeration?
My mother who owns a private company asked me if I could fly her to a convention. She asked if it was possible if the costs of the plane rental could be invoiced to her company. Since I only posses a PPL (EASA) I was wondering if I was allowed to perform this flight since you're not supposed to do commercial flights. I won't get paid anything for this flight so I don't think there would be a problem but just want to make sure.

Hi GillesDB. I edited the title of your question to try to better summarize what you are asking. If you feel my edit changed your intent in any way, feel free to [Edit] further, or to roll back the edit.

The body of the question doesn't match the title.  What do you mean by "invoice"?  Because this typically means to bill, to get paid...

In the UK, at least, the rules specifically state:

Privileges and limitations:
    A holder of a PPL may, for compensation or hire, act as a crewmember of an aircraft in connection with any business or
  employment if—
a. the flight is only incidental to that business or employment; and
b. the aircraft does not carry passengers or property for compensation or hire.

Despite what this may sound like, this means you are not allowed to be paid for flying unless you happen to be an employee and flying for work -- e.g. an archaeologist (with a salary from University X) flying yourself and a colleague to a dig site (while employed at the University of X -- thus flying for compensation [because you are paid, indirectly, to do this] but incidental to the employment [the University of X is not an airline, and the colleague you are with is not a co-pilot or paying passenger]).
I have always been taught that the safest thing to think is this: As a PPL, you cannot fly for compensation, and each of your passengers at most has to contribute not more than their "fare" share of the cost of the flight.
By invoicing your mother for the cost of the plane rental you would not be contributing that value in kind, and thus would be in violation of this rule (with rather unpleasant consequences, should you be caught -- ranging from losing your license to a minor criminal conviction). Moreover, the fact that you mentioned the word invoice makes me think that your mother's company would be expecting you to provide a service -- all of these are commercial terms, and alarm bells would be ringing in the mind of any examiner looking at this from the outside, as it starts to really sound like you're providing a service for hire.
Ignoring for the moment that many organisations have rules about doing just the following with family members, I suggest instead keeping all of the receipts of your legitimate expense for aircraft hire -- Hobbs hour fees, fuel, landing, whatever -- and then getting your mother to claim exactly half their value as a business expense. That at least makes it very explicitly clear that you are paying your fair share of the cost of the actual flight, and highlights the nature of the compensation as covering an expense, not a fare.

Does EASA have a "common purpose" requirement like the FAA does? In the US, I can't split expenses with a passenger if the passenger's purpose is to attend a conference and my purpose is to get a sandwich.

@TannerSwett: As far as I can tell, no. Paragraph 7 of the Air Navigation Order states " For  the  purposes  of  this  Order,  “commercial  operation”  means  any  operation  of  an  aircraft other than for public transport— (a)which is available to the public; or (b)which, when not made available to the public, is performed under a contract between an operator and a customer, where the latter has no control over the operator, in return for remuneration or other valuable consideration."

My understanding of the question is that the invoice would be issued by the owner of a rental plane, or in other words, that OP's mother's company would rent a plane and OP would then fly it.

So if the OP's mother would employ him in her company and require him to go the same convention, the OP could "incidentally" fly both of them there, correct?

them there, correct? – DeltaLima 1 hour ago
@Terran Swett, what if they both planned to attend the convention, but one changes their mind after they get there?  What if the one not attending buys a sandwich from a vendor at the conference? Or what if the one attending also decides to get a sandwich?

@DeltaLima I believe so, yes if and ONLY if the company hired the pilot for activities other than piloting -- the activity of flying has to be "only incidental" to their employment. It would be difficult to convince any reasonable person that you were hired for a week as a well-paid secretary who just happened to come with with a pilots' license as opposed to a pilot side-stepping the rules.

@MichaelHall This is what a world of case law helps us to interpret. CAA rules are ultimately legally enforceable and it is -- as ever with the law -- the question of intent that matters. Rules-ninjaing may work well with Dungeon Masters and level 9 Wish spells, but it doesn't work well at all on judges. If the pilot had ten years' experience of working for the company, spent the entirety of the convention in his room with a headache and went home, it's probably fine. 10 days experience; not so much.

@Landak, I completely understand intent, which is precisely why I get so frustrated when the rules ninja pendulum swings so far to the hyper conservative side that people are afraid to take a friend somewhere for a burger.  There would probably need to be extenuating circumstances for the FAA to haul you into court over a question of which of two friends had the best reason for taking a trip...

In the UK at least if you were flying yourself to the convention for the purposes of legitimately taking part for the purposes of busines then yes, you could get paid for the flight. If you are flying someone else for the purposes of their business then no, you can't. I believe EASA has the same criteria, however every country may have a different interpretation, so you'd have to be more specific, the country being the issuer of your license.
You could fly her to the convention and she could pay half the costs, reimbursed by her company as a legitimate expense, you'd have to pay the other half out of your own pocket. Still, that's half the costs paid.


text:
More information on PanAm's first trans-Pacific flight
I have came across this answer, about PanAm's first trans-Pacific flight (SFO-MNL route via HNL, MDY, AWK and GUM). For the text, I'm working on, I was wondering, if there is any source that can provide more information on this route.
Literally:

years of operation,
approx. times needed to flight each segment,
approx. break times (refueling?) times at each mid-point,
was passengers allowed to leave the airplane during each break?

I'm also interested in getting answer to a question that might be harder to answer (too broad?). How it was possible to service / refuel airplane on airports marked as uninhabited in the original answer (MDY and AWK)?

[tag:pan-pan] is not appropriate here.

There are many sources of information about these flights that you can find by doing an Internet search. For example, I just used "panam clipper flight sfo to mnl".
The following links should get you started:
In addition to some aircraft information, this link has a schedule image about halfway down the page:
https://www.pacificaviationmuseum.org/pearl-harbor-blog/pan-ams-pacific-clippers/
This link has more Manila-specific info, with a video.
http://www.lougopal.com/manila/?p=1463
The following link, in the paragraph "Building Bases Across the Pacific" will answer your last question regarding MDY/AWK:
http://www.clipperflyingboats.com/transpacific-airline-service


text:
How do aviation regulatory bodies relate to each other?
I am trying to make a overview how regulatory bodies in aviation safety interrelate. Maybe something like a  hierarchy. I would start with ICAO and IATA, but where comes then for example FAA, CAA, LBA? Thanks for trying to help me...

Hello Ayiko, welcome to aviation.stackexchange.com. A few related questions have been asked already, you might find the answer there.  For example: What is the difference between ICAO, JAA, FAA, EASA, and CAA?

I could not find my answer in the article you provided. I do not need a explanation of those organisations but some kind of hierarchy. Who would be on top of it (ICAO, IATA), ater that for example we move towards European regulations and in the end government and local authorities.


text:
What was wrong with my answers to how to deal with low volt annunciator, and icing, both in IMC/IFR?
I have questions for emergency situation in IMC.
I was asked about low volt or icing condition IMC from my school's checker.
The checker said "if you see low volt annunciator on PFD how can you deal with this problem under IFR flight?" So I answered "first contact ATC, and request radar vector to nearest airport and then, I will follow the check list for low volt annunciator." However, the checker said this answer was wrong.
Also, I got a similar question from the checker which is icing condition during IFR flight.  "When you face on icing condition under IFR flight, how can you deal with this situation?" So I also answered "first, I will turn on pitot heat, deforster and cabin heat, After that, I will do climb or descent to get warm air to rid of icing and try to get VMC condition. However, I will consider the altitude which is be higher than MEA. Also, I will do follow the check list for icing. If the problem is not solved, I will let ATC my problem, and request radar vector to nearest airport." But, the checker thought this answer was wrong too.
Is there any problem from my answers? Or could you let me know how I can deal with this low volt or icing situation in IMC?
Thank you very much!

What kind of airplane is it?

I edited the title of your question to try to better summarize what you're asking. Do note that IMC and IFR are not the same thing, and IFR does not imply IMC.

Did you ask the checker, or your instructor? Maybe there are some very specific answers that your school is looking for?

my airplane is C172S G1000

I asked what answer was, but the checker did give it to me.

remember the Aviate, navigate, communicate bit in your PPL? I'd be looking to keep the plane level, then try and sort out the issue, (recycle altenators, anti ice etc), then tell ATC you have an issue, what youve done about it so far, and what you want from them, inc. possible diversion, alt change etc.  You cant have that thought through conversation with ATC, unless you have the planning before the flight, and an update for yourself after the checks.

Based on a 172S G1000

I wouldn't say your answer for the first question is wrong, but your steps are out of order. Before contacting ATC you need to verify the issue via whatever the POH says. On a 172S that means you will cycle the alternator switch and verify low voltage on the G1000 and whether or not the battery is charging. Do realize that the G1000s have a backup battery that provides x amount of backup time and it should have already been tested in the pre-flight and set to arm, if you verify the issue then limiting battery load and  contacting ATC would be the next step, never the first, and the value of backup time should be known and planned around(can't recall at this time, sorry).
I think this question is more semantics and specifics, he/she may not have liked climbing or descending as your only answer really, getting out of icing is the most important thing whatever the direction is, but I agree in general with climb/descent based on information. Asking for an altitude change I assume is implied when you say climb or descend. What you describe here is pretty text-book as far as dealing with icing to my knowledge.

Welcome to Av.SE.  Good advice to figure out what you have before talking to ATC... Aviate, Navigate, Communicate!

I don’t know that your answers are wrong, but here’s how I’d answer:

Low voltage:  assuming no standby alternator, tell ATC you’ve lost alternator.  Check the CB for Alt and reset it once if it has tripped.  Assuming it doesn’t hold and if in IMC, declare an emergency and tell ATC you want out of IMC ASAP before your electrics die, so divert or descend to leave IMC if possible.  If not possible, divert to the closest airport with an approach and land.  Shed load on the battery by shutting down all unnecessary equipment (although it may not be much in IMC).  If not in IMC, divert to an airport with services if close by and consider getting the phone number of the tower to use your cell phone in case the radios die.

https://www.boldmethod.com/learn-to-fly/aircraft-systems/what-happens-when-your-alternator-fails-during-flight/

Assuming non FIKI aircraft:  Pitot heat and defrost as you said, carb heat too.  If no carb, watch MP and consider alternate air if induction ice appears to affect the engine.  If in widespread IMC (ie, not in a localized cumulous cloud, tell ATC, and consider a 180 and return to non icing conditions.  Also consider a new altitude to non icing conditions. Consider the “out” that you planned for in your flight plan (you did have outs, didn’t you?).  Maybe he didn’t like that you were changing altitudes without telling ATC?


text:
Name of this part of jet engine inlet

I can't find any name of it. I see it on some gas turbines but not all of them.
Edit: Found them, they are called struts.

No, I don't mean IGV.  IGV are more distingiushible and there are many more things to whole surronding. This one that I'm reffering to are more like support fins, for stabilization or additionall rigidity? I'm not sure, they are usually omited in any descriptions.

Like IGVs usually has some mechanism to change it's position. This on the other hand is for sure static also the air passages are huge between them as there is only 6 of that.

Those are the structural elements (struts) holding/supporting the cone in the middle in respect to the outer case. As a side effect they also straighten the airflow entering the compressor. On the Olympus (and most probably on other engines as well) they were also used to let hot air flow toward the cone for anti-icing purposes (A1 in the following cutaway - cutaway source):

In that cutaway it's also possible to see that the cone, in turn, holds the shaft (through the roller bearings) of the low-pressure compressor.

Thank you, that's an answer that i really looked for.

@AdamDutkiewicz: you're welcome


text:
Is the centripetal acceleration when an aircraft turns related only to the load factor?
My question is about aircraft load factor and how it relates to turning ability.
I've recently come across this chart for the F-16 that shows the turn rate in degrees per second and the load factor when doing a sustained turn at different speeds.
I've always knew the load factor was the sum of the forces that act perpendicular to the aircraft (apart from weight) divided by the weight of the aircraft.
If load factor (when speed is constant) is the only thing related to the centripetal force, then the centripetal acceleration in Gs is equal to the horizontal component of the load factor.
This means that in a sustained turn (where altitude does not change so the vertical component of lift is equal to weight) that horizontal component will be, using pythagorean's theorem, : $ F_c = g \sqrt{(n_z)^2-1}$ , where $n_z$ is the load factor and g is 9.81m/s^2 .
From this we can derive that angular velocity in deg/sec is equal to: $ ω =  \dfrac{g \sqrt{(n_z)^2-1}}{V}  \dfrac{180}{π}$ .
When looking at the F-16 chart (Ps = 0 line is the one to look at for constant speed) thought, this results do not match.
Using this formula, for example, at mach 0.3 (~97.22 m/s) the F-16 does about 2.95G of load factor, which results in 16.05 deg/sec of turn rate, but the chart shows a little over 17. In general the lower the speed (so higher the angle of attack) the bigger the difference between the formula and the chart.
Any thoughts? Maybe the Load factor in the chart is instead the normal Load factor $ N_z $ instead of $ n_z $?

The altitude is sea level, it is written in the picture

Might be the extra engine thrust at higher angle of attack, the lift vector is smaller.

Isn't the sin(AoA) component of thrust already included in the load factor thought?

@Giovanex For a standard day the mach number at sea level is $340.3 \frac{m}{s}$, therefore Mach 0.3 is equal to $0.3\cdot 340.3 \frac{m}{s}=102.09$.
However, I actually think your formula is wrong...

But it am not 100% sure where...

What do you mean by "Maybe the Load factor in the chart is instead the normal Load factor Nz instead of nz?"  What do you mean by "normal Load factor"?

The load factor in this Technical Order is indeed normal load factor Nz, or body Z axis g's. See also https://aviation.stackexchange.com/a/104783/71947

@U_flow with 102 m/s the discrepancy would have been even higher… formula using load factor n was right, but as LKQCN101 said the chart showed normal load factor Nz, which is different from n

The F-16 uses normal load factor (Nz) in the flight control system, and also on HUD to be read by the pilot. When you watch closely to the 1g line of this chart, you can notice that it even got positive turn rate.
Normal load factor Nz is the sum of forces (apart from weight) that act perpendicular to the aircraft body X axis (Xbody), divided by the weight of the aircraft. Those forces are called normal force, and can be calculated by (Total Drag * sinα + Total Lift * cosα). See equation IV-34 below.
This is not to be confused with load factor $n$ which is the sum of forces (apart from weight) that act perpendicular to the relative wind, divided by the weight of the aircraft.

Images are from DTIC ADA 189675.

Thank you very much! Did a quick calculation and, in a steady turn n_z ends up being N_z/cos(AoA) , and it matches perfectly the results of the graph

@Giovanex If this answers your question well, please consider accepting this answer.

@Giovanex It's not as simple as dividing by cos(AoA). From the equations, load factor = (Total Lift + Thrust * sinα) / Weight, while Nz = (Total Lift * cosα + Total Drag * sinα) / Weight. So they’re not directly related.

@LJQCN101 in a sustained turn at constant speed and altitude:  thrust cos(AoA) = drag . By writing drag as Thrust cos(AoA) in the Nz definition you get: Nz = (Lift cos(AoA) + Thrust cos(AoA) sin(AoA) . One can rewrite this as: Nz = (Lift + thrust sin(AoA) ) cos(AoA) and from there Nz = nz cos(AoA)

@Giovanex Yes you're correct, it applies when Ps=0.


text:
The relation between aerodynamic center and lift
On the internet, I found two separate definitions for the aerodynamic center. One was "the point where pitching moment is constant regardless of angle of attack" and the other was "the application point of lift". I tried to figure out how the second definition can be made from the first and I thought it was because since pitching moment is force multiplied by distance, if the AC is the point of application of lift, it wouldn't change from AoA. However, I still don't understand a few things.

Since lift is caused by airfoil shape, doesn't a change in AoA cause both the main wing and tail wings' lift to change? Or do both forces change by the same amount so that the application point of lift stays constant?
Even if the two lift forces change by the same amount, doesn't gravity contribute to pitching moment? I'm almost sure gravity doesn't change from AoA.
Or should I understand the first definition as the lift on individual mass points not changing from the AoA?

TLDR, how does the pitching moment not changing from AoA at the AC make it a point of application of lift?
P.S. Please explain any new technical terms and correct me if I'm wrong about anything, as I'm a middle schooler who's new to this field.

That may help: What is the difference between centre of pressure, aerodynamic centre and neutral point?

"the point where pitching moment is constant regardless of angle of attack"

is called the neutral point or the aerodynamic center.

"the application point of lift"

is indeed the center of lift or center of pressure.
Please do not believe outright what you read on the interwebs. So many people get the details wrong because they simply copy from others. Instead, try to comprehend what happens in detail and ask yourself every time "can that be right?". You'll be surprised how often the answer is "no".
Please follow the links for the requested explanation of the terms. They can be applied to a single airfoil (2D flow), a whole wing or the complete airplane (both 3D flow), each time with different meanings, as @sophit correctly mentions.

You'd better specify that the terminology can be applied to the whole aircraft, only to the the wing or to the airfoil. With different meanings.

@sophit Good idea to do it already here, even though the linked answers do it, too.


text:
How can an ATC choose the right flight level and heading for airplanes?
I don't understand how air traffic controllers can choose the right flight level and heading for airplane when they are in the sky or they're approaching the airport to land.

During the enroute portion of the flight at cruising altitude, pilots will have filed a cruise altitude and route based on airplane performance and weather. ATC will not need to change this unless the pilots ask to deviate or there would be a separation issue. Separation will depend on the local regulations and type of airspace and aircraft involved. For airliners this is usually 3 miles laterally or 1,000 feet vertically.
Pilots may request deviations from their filed route due to weather or other reasons. ATC will look at other traffic in the area and determine what changes can safely be made. ATC may also need to give altitude changes to keep them clear of other traffic. If two planes are converging at the same altitude, at least one of them would need to climb or descend.
When arriving at the destination, many airports have stardard terminal arrival (STAR) procedures that pilots use in their route and may give route and altitude instructions. ATC will also have standard procedures for routes and altitudes that will allow arriving aircraft to descend without interfering with departures or other airspace in the area.

This seems a broad question to me, as the answer to both questions is it depends and answers can expand endlessly. As the community hasn't voted it as "too broad" I will attempt to answer, although I'm afraid that it will be a "stapling" of other questions of this site.
ATC 101
Let's start by clarifying one common misconception. There is not "one ATC unit"  there are several: When a plane is close to a controlled airport, it's controlled by tower. After takeoff, by approach/departure; during cruise by en-route control ("Centers" in the US, "ACCs" in Europe and I don't know for the rest of the world) and during landing it's again approach/departure, and then tower again. For more information you can have a look at this answer which explains these concepts in depth.
This is irrelevant to the question but why do I mention that? Because an approach/departure controller's job is significantly different than the one in ACC. As a result they assign headings and altitudes in a different manner.
Altitude
Valid altitudes
abelenky in their answer mentions the "even-odd rule" for altitude assignment which is correct. But if want to go deeper, this is not entirely true: above FL410 ("41000" feet) flight levels are every 2000 feet. So 410 is the "odd" and 430 is the "even" (ie the westbound). And that was after RVSM. Before RVSM, flight levels were every 2000 feet from FL290 up to FL410. and every 4000 feet above FL410. Again the "even and odd" was redefined. More information on RVSM on this answer.
There are cases where the pilot can request to be exempted from RVSM. Severe turbulence is one case, although I've heard that disengaging the autopilot is not the first option; it's an altitude change request I guess mostly because ATC can easily decline you the request to be exempted.
Also air traffic controllers can offer to pilots an opposite(1) flight level (specifically mentioning opposite in the phraseology) where the pilot can either accept or refuse.
Altitude assignment
Usually when a flight receives a departure clearance, it is assigned a runway, a SID and an altitude. This altitude might be dictated by many factors like the SID itself, the terrain around the airfield and the traffic around the airfield at the time of takeoff. For the last case, the controller's judgement call is required.
After departure the controller will try to clear the flight at the predefined handover altitude with the ACC. If that cannot be reached on time, a coordination needs be done between the 2 controllers.
Climbing
When the aircraft is in the ACC's control, the controller will again try to direct the aircraft to its final requested level. Usually, upon first contact of a departing flight the controller will ask foobar flight say final requested level and the pilot will report it back. The requested flight level (RFL) is included in the flight plan, but for some reason that I've never asked why they ask the pilot when they get them on frequency.
Descending
After that and until the top of descent there is no significant change in altitude. At the top of descent the pilot will request a descent and the controller will grant it whenever it's safe and possible. And then the reverse process starts: get the flight at the predefined altitude for handover with the approach, and then the approach will try to descend the flight to the appropriate altitude for engaging the ILS or other instrument approach procedure.
Heading
Departure
Before departure a flight is assigned an SID and they are supposed to follow it, unless they receive an instruction from the controller to deviate. When discussing with air traffic controllers in LGTS, they told me that the majority of the flights are assigned a "direct" to the TMA boundary. They assign a heading only if there is traffic in the vicinity and want to steer the departing flight away of it.
Arrival
During arrival as it is correctly mentioned by fooot's answer a flight is (usually) assigned a STAR, which they follow in order to engage the IAP that will get them safely to the runway. In airports with RADAR service though, the approach controllers are vectoring the flight in order to create a stream of aircraft, a queue for landing. In order to keep this post short (too late I'm afraid) and because I don't want to repeat myself, I invite you to read my answer on the topic here. Then you can see if you still have blurred areas and you can post a new and more specific question.
En-route
During en-route control the flights fly on airways. The routes they follow though are not always great circle arcs. So very often the pilots are tempted to request a direct to point to save some miles, and along with that fuel, emissions and time (so everybody is happy). The controller again might or might not grant the direct depending on the situation.
Separation
All the above make the profession of the air traffic controller sound very easy: just a cool and relaxed guy giving predefined altitudes and headings. Nice... But that's far from the reality. Many times things don't go as planed and flights on the same altitude converge and the controller has to take actions. They have to evaluate each case and decide which technique they will follow to resolve the conflict: altitude change or vectoring?(2)
Even worse there might be 2 flights not on the same altitude climbing or descending and still converging and these are more difficult to detect. Remember when I mentioned the differences between approach and en-route controllers? Here is a good opportunity to explain it: An approach/departure controller (usually) has a smaller area to control than the ACC controller. Both vertically and laterally. That's why they can grant a climb from 4000 or 5000 feet to the upper limit on the TMA (which might be up to FL250) more easily. But an ACC controller has to be more careful: once they receive the flight they have to climb it incrementally. At higher altitudes the climb rate degrades and the speed increases rapidly. The plane will take longer to reach the RFL. If they grant the RFL very soon, how can they be sure, that many nautical miles away (might be from 100 to even 200 depending on the circumstances) there isn't an opposite or crossing flight that will come by and bite them?
Believe it or not this is the short version of the answer. You can take each and one of the paragraphs and expand them to infinity. Feel free to post new and specific questions if you would like to know any details. As you can also see from the links, most of the questions are already asked, so feel free to make a search first. I hope this is helpful.
(1) westbound FL for an eastbound flight and vice versa
(2) and some times speed control but let's keep it short(er).

@Toby Speight, thanks for making the effort to read and correct.

Note that at longer range, aircraft tend to step climb. As the plane burns off fuel and gets lighter, it can climb higher and it is more efficient if it does. So the filed altitude is not actually valid for the whole flight. That's likely why the controller often ask (well, if they don't, the pilot will).

@JanHudec I think that I've heard them asking for flights that just got out of the TMA (departures). Let me see if I can ask and find any details on that.

There is a rule that planes flying East should travel at odd-thousands of feet (19,000; 21,000; 23,000; etc), and planes flying West should travel at even-thousands (20,000; 22,000; 24,000; etc).
There are wind-forecasts made daily using weather models, radar, balloons, and other observations to figure out which way the wind is blowing at different altitudes.  Whenever possible, planes try to fly with a tailwind to cover more ground faster.
Pilots can request the altitude they want to be at, and provided ATC sees that will not put them too close to another airplane on radar, a pilot request will generally be granted.

What's the minimum distance that an atc may keep between 2 airplanes?

Physics recommends anything above 0.

Minimum distance depends on the size of the 2 planes. 2 large airliners can be closer together than say any airliner and  my small 4 seater - their wake vortices can upset the heck out of  small plane.  A super-jumbo like A380 can have the same effect on larger planes, like a Gulfstream and probably as large as a A320 or B737 or B787. The bigger they are, the more disturbance and the longer lasting it is.  I avoid larger airports, as you get stuck waiting a really long time waiting for disturbed air to clear, Large airliners in trail can be 3-5 miles behind each other depending on size.


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What airspaces are the Florida Everglades?
If I'm flying through the Florida Everglades, what airspace would it be?

It depends on your location and altitude. You can find any of the classes of airspace above the Everglades.

The Florida Everglades covers a vast area.
(link)
I found parts of it are within Class Bravo, Class Charlie and Class Delta, Class Echo, and Class Gulf.

And if you go high enough, Class A.


text:
What is Squawk on radar tracking websites?
I have been noticing squawk on virtual radar, anyone have any idea what this is?

A picture or example of the site/area you are seeing this on would help greatly... Are you sure it isn't "squawk"?

https://staging.spee.ch/f9182d8ad3aa21c44f9bc312f3cd7a1247339111/Screenshot20181018-141536.jpg

The 4th column from the left in the picture.

Thanks for the help. I will go and have a read up on that now but it looks to be what I was after.

See https://en.wikipedia.org/wiki/Air_traffic_control_radar_beacon_system


text:
How would an aircraft fly PIKES ONE departure procedure of Denver Airport?
I was examining FAA's departure procedures and I noticed PIKES ONE SID (chart and continuation) which serves Denver Airport.

In the description, it states:

TAKEOFF ALL RUNWAYS: Fly assigned heading for RADAR vectors to assigned route. Climb and maintain 10000 or ATC assigned lower altitude. Expect filed altitude 10 minutes after departure.
LOST COMMUNICATION: If no transmissions are received within one minute after departure, maintain assigned heading until 7000 feet, then climb to filed altitude via direct DEN VOR/DME, thence via assigned transition.  If filed altitude is above 10000 feet, cross DEN VOR/DME at or above 11000 feet.

What troubles me is that DEN navaid is (obviously) very close to the airport, so I am not sure how an aircraft would depart from the airport via a runway very close to DEN, for example 07/25, and have enough space in order to reach DEN. In addition, based on Lost Communication, an aircraft would climb until 7,000 feet and then go direct to DEN, even if it has already surpassed DEN (by departing, for example, via runway 17R/35L) and theoretically it can just follow the assigned route by skipping this navaid.
In other words, is the aircraft obliged to fly to DEN before following the assigned route under any circumstances and, if yes, what would be a possible flight path in case of a runway that is really close to it?

It seems like this route is mostly used for flights to KALS. You can see a list here. It looks like the typical route is an assigned heading on takeoff and then direct SOLAR.

Let's treat the "normal" and "lost communication" cases separately.

Fly assigned heading for RADAR vectors to assigned route. Climb and maintain 10000 or ATC assigned lower altitude. Expect filed altitude 10 minutes after departure.

The essence of this is that on departure, responsibility for navigation rests with the air traffic controllers, not the pilot. The controllers will issue headings and routes to fly in order to keep the aircraft separated from other departures, arrivals, and other traffic. Once clear of traffic, the controller will issue instructions on how and where to rejoin the cleared route. At this point the pilot takes over responsibility for navigation along the cleared route.
Usually, it goes something like this. The departure will be assigned an initial heading, often the runway heading: "runway 17R, fly runway heading, cleared for takeoff." The aircraft flies this assigned heading. The aircraft will then contact the departure controller. The departure controller may continue assigning specific headings in order to separate the aircraft from other departures, arrivals and other traffic. Once clear, the controller has some options. They can clear the aircraft direct to a convenient fix/waypoint or NAVAID on the aircraft's flight plan ("Proceed direct ADANE, resume own navigation") or they can say something like "Fly heading 130, join the Denver 159 radial, resume the departure." It's up to them, but they will issue some kind of instruction that results in the aircraft joining its cleared route.

LOST COMMUNICATION: If no transmissions are received within one minute after departure, maintain assigned heading until 7000 feet, then climb to filed altitude via direct DEN VOR/DME, thence via assigned transition. If filed altitude is above 10000 feet, cross DEN VOR/DME at or above 11000 feet.

If communication is lost, the pilot should do the following in order once it is realized that communication has been lost.

Fly the last assigned heading until reaching 7,000'.
Turn (back toward the airport and the DEN VOR) and fly to DEN.
Comply with the crossing restriction (make sure you reach 11,000' before getting to DEN if your filed altitude is above 10,000').
At DEN, turn outbound on the appropriate (filed/cleared) transition leg.
Keep climbing to the filed altitude.

It is likely that some short amount of time will pass before it is realized that communication has been lost. The aircraft will travel some distance away from the airport during this time. The aircraft must also continue until it reaches 7,000'. So by the time it would become necessary to "proceed direct DEN," the aircraft will not be "right next to it" and a turn direct DEN is reasonable.
If you departed runway 25, your route might look something like this (not to scale!).

Shouldn't the flightpath in that diagram be passing directly over DEN and then turning to the transition leg, rather than turning back well short of DEN?

@Sean That's a good question and might be worth a dedicated post here. What I've drawn shows "turn anticipation" and is what any RNAV system I've ever used will do (Garmin, Rockwell Collins FMS, etc.). Airway protected volumes include flyover overshoot protection for non-anticipated (flyover) turns. Aircraft without RNAV or DME may not be able to turn early and must fly-over. Either way, as long as you stay within the protected volume, it doesn't matter. Note that some waypoints in actual RNAV procedures are explicitly fly-over instead of fly-by.

That said the turn should definitely at least be drawn closer to DEN. It looks premature and cuts off too much of the corner. I drew the spline in by hand as a Path in Photoshop so it's not at all precise. :)

In the old days of /A navigation, an aircraft was expected to fly to the NAVAID before making the turn. Modern FMS, however will cut the turn short of the NAVAID, and fly the aircraft's best performance radius to the new course.


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cost effective air power
I came across an interesting speculation that basically wondered if it would be more cost effective to use cheaper jets as fighters in greater numbers. I thought it may be plausible, but I wonder if there is someone who knows for sure.

If this is about military strategy and economics, then this is off-topic. A specific question about the design differences of fighters vs. business jets could be a better fit here.

I would go even further: If you take the same budget and buy motor gliders, you could fill the sky with them. All the resulting collisions with them will wear down any enemy air force quickly.

Can you put a price on a human life?

These days, fighters don't fight so much against each other as they fight against surface anti-air defences.
And those Citations won't stand a chance against even simple AA gun battery. They don't have manoeuvrability to zigzag to make them harder targets, don't have manoeuvrability to fly at tree-top heights to minimize time in covered space and have huge radar cross-section, so the targeting radar will lock them from miles away.
Avoiding these threats is what makes the fighters expensive.

The short answer is no and frankly the article says it all in the first paragraph...

Now, I don't claim to have any expertise on aircraft design nor to have done any serious research on this subject,

Not to mention that a new citation X costs 22.5 million (according to wikipedia) and the Mustang comes in at a mere 3.28 Million not the 2.5 million he seems to think. But still a a bit cheaper than some fighters.
But lets discuss it for a minute. First off military jets are far more complex aircraft and are capable of maneuvers that civilian aircraft simply are not. The cost of the jets is related in part to the complexity of actually building one and the fact that they often use simply more expensive materials like Titanium in simply more places than a civilian aircraft.
The author goes on to make some egregious claims about strapping weapons to a Citation. While this may be possible it would most likely cost more than anticipated not to mention large airframe modifications. If you simply are asking "can you put some big guns on a citation" the answer is in a since yes. Could you successfully dog fight with a citation, I doubt it.
Lets look at his comparison with the Bede BD-5J, your limiting factor here is simply gross weight. In a plane that size you may be able to carry a 6-shooter (and if  you have been dieting all week) 6 bullets for it. Not making it a very effective fighter. This will come into play with the Citation as well but I dont know the loads they can haul so Im sure how much you will limit it.
The argument here of masses with lesser technology holds little merit since in a dog fight situation the fighter is going to be simply faster and more maneuverable and even if you had 10000 Citations with guns the fighter can simply out run/maneuver them.

Add to that, I question how much dog fighting is an applied battlefield skill anymore, given over-the-horizon radars and long range smart-missiles.

@abelenky maybe not applied that often but in a real conflict, it will come to that.

While I agree that little dog fighting may occur it was worth bringing up.

The little BD-5J may not carry much weight or have much range, but with a little work it can be made invisible to radar. That's why the US and NATO military has been using them as cruise missile surrogates for years now. http://freedomjet.com/


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What do these double Class Bravo airspace floor and ceiling limits mean?
While browsing SkyVector I came across these double Class B airspace limits within the same section (is that what you call it?). I'm wondering what it means and what the difference is between this and FL145/SFC.

https://skyvector.com/?ll=36.81236324400328,-4.208404530018495&chart=301&zoom=2

Simply a coincidence that you're familiar with the Malaga area @abelenky?

Welcome to aviation.SE!

Thank you @Pondlife !

@Basaa:  I read the snippet of Morse Code on the VOR ID (--   --.  .-).  MGA is the ID for 5 different points worldwide.  It was easy to find the right one.

@abelenky 200IQ confirmed haha

The way SkyVector shows airspace is subtly different than shown on FAA charts. Whereas the FAA shows the combined limits in each area, SkyVector shows the limits once for each layer, even where layers overlap.
So, what you are probably seeing here is one area of FL145/35 on top of another area of 35/SFC, possibly disjoint but the labels for both areas just happened to end up near each other. Or, it may be two areas with the same boundaries but different owners or airspace classes. As a result, it’s often difficult to figure out exactly which area(s) each label applies to.
Note that while SkyVector uses official maps from the FAA in/near the US, the rest of the world is computer-generated and not nearly as useful, especially since other countries often use airspace classes in vastly different ways that can’t be represented well in SkyVector’s pseudo-FAA style. Notably, they use blue for all classes, which often confuses folks used to the FAA’s color scheme.
According to the Spanish AIP, they are indeed two stacked airspaces; TMA SEVILLA AREA 3B and TMA SEVILLA AREA 3C. For example, in 3B (the higher one):

VFR traffic is not allowed, except for State aircraft, helicopters, medical and rescue flights.

Official e-chart here: https://insignia.enaire.es/

Super useful stuff. Thank you so much for the help guys! Enjoy your weekends!

They do not use just blue, they also use gray for TRAs and TSAs. Also, our AIP also draws everything in blue https://aim.rlp.cz/vfrmanual/actual/lkpr_text_en.html  I do not think it is inherently bad.

@VladimirF Can you give examples? I’ve never seen anything but blue on SkyVector. Using blue everywhere is not bad per se, but it does confuse US pilots who are used to blue only being used for class B.

@StephenS Yes all controlled airspaces are all blue. But gray is used for dangerous spaces, restricted spaces and similar. I have not seen colour coding for different airspace classes in any European AIP. Nor have I seen much class B either...

@VladimirF SkyVector uses blue and magenta ticked lines for SUA, same as FAA. I don’t see gray lines anywhere.

If you call it magenta, so be it. There is no magenta colour in my language (we are the side that lost there...) so I am not used to naming this colour this way.

authors: Vladimir F Героям слава


text:
How can I approach analyzing the basic performance characteristics of an unknown aircraft?
I am working on a project for one of my classes. My group and I have been given information on an unknown aircraft, and we must find the max velocity, max R/C, max range, and max endurance of the aircraft at sea level assuming max fuel and payload.
We know its max velocity at an altitude of 21500ft, its wing span, platform area, fuel tank capacity, engine fuel flow rate, payload capacity, empty weight, C(Do) and that its airframe is similar to the A-10 Thunderbolt 2. We are having trouble figuring out how to actually calculate these values. We have been able to calculate it's AR, chord, Oswald efficiency factor, and Reynold's number at altitude, but we don't quite know where to go from here.
We think we might have to calculate the velocity at sea level using the $V(alt) = V(SL)\cdot\sqrt{\frac{\rho(SL)}{\rho(alt)}}$ formula or that we might have to try and solve for the angle of attach by assuming that L=W at altitude and solving backward from L=qSC(L). We are basically lost after this point, though.
If anyone could give us a hint on the correct direction to go from here or let us know if we are approach this problem in the correct way that would be much appreciated! We just need a hint, though, because we want to try and figure out as much of this as we can on our own!

What you need are the Breguet equations. What data are you missing to evaluate them?

Please use the search terms "quadratic polar equation" and "Breguet range equation" and read the answers. Let's see how far you get with those. What you are still missing is the engine thrust over speed dependency, so I wonder whether you have more information than you think.


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How come the DC-8 plane can withstand +15G from turbulence, but newer planes can only withstand 20% of that amount?
Source - https://www.weather.gov/media/zhu/ZHU_Training_Page/turbulence_stuff/turbulence3/turbulence.pdf
(Scroll down for photos)
I figured out how many G's the cargo jet took by looking at the distance it traveled vertically (500 feet). The turbulence lasted ~10 secs. Most turbulence spikes last half a second or so, so I did some calculating -
9.81 = 1 G (normal gravity)
9.81 x 15 = 147.15 (15 G)
147.15 metres into feet =  482.77 feet.
Within a second the DC-8 would have dropped (nearly) 500 feet under 15 G of force.
Half of its wing ripped off and an engine was missing but it stayed intact enough that it landed safely.
So now we know that turbulence can produce forces in excess of 15 G's, why are newer planes only certified to handle 2.5 G? I saw a Boeing spokesman say the worst turbulence only gets to around 2.5-3 G.

You might be interested in http://www.avialogs.com/index.php/en/aircraft/usa/douglas/dc-8/dc-8-operations-manual-american-international-airways.html. Specifically, that's an operations manual for a DC-8 (N818CK), issued in 2000, which clearly (page 1-5, document page 33) specifies that the maximum load is 2.5 G flaps up, 2.00 G flaps down.

Something is off about your calculations... 15 G's for an excursion of 147 meters would happen in about 1 second. Remember, it is 9.81 meters/second/second. 500 feet in 10 seconds is 50 feet/second, the calculation should give you 50/32 = ~1.6g's. Astronauts getting launched on the Soyuz usually only experience about 4 g's...

You have to remember turbulence isn't smooth. It's going to be sharp ''bumps.'' A bump can last a second, so it is implied within the span of a second the turbulence forced the plane to drop 500 feet. I've played numerous simulators to confirm this is correct. Turbulence isn't like a gentle children's roller coaster ride - it hits the plane in a series of irregular spikes.

I can't believe that the aircraft moved 500 feet in 1 second, and nothing in the linked PDF seems to suggest that. 500ft/sec is 340mph, so unless the aircraft pointed straight down, I just don't see it.

It says right in the pdf the plane encountered extreme turbulence. There were also extreme downdrafts and updrafts in the area because of the correlation between the mountains and the jetstream at the time.

Well, if you've got an updraft at one point, there's a downdraft pretty close by. That's one thing my flight instructor made sure to point out to me quite clearly the first time we encountered one while in the air. It's made me go around on more than one occasion when encountering an updraft on final; not because of the updraft per se (that's managable), but because of the downdraft that's out there somewhere nearby, just waiting to hit you with a sledgehammer if you get unwary.

Before jumping to conclusions, let's look at the numbers:
The duration was about 10 seconds, the altitude excursions was 500 ft.
There is no way we can derive a 15g acceleration from that.
It could have been, for example, a 3g acceleration over 2 seconds, resulting in 200 feet excursion, followed by 0.2 seconds coasting after which the pilots levelled off with 2.3g in 2.6 seconds. The resulting excursion would be 500 feet. If the processes then repeated in the other direction, the total time would be approximately 10 seconds, the maximum excursion 500 feet and the maximum acceleration  only 3 $g$.
But the fact is we don't know, it's pure speculation.
Another point of discussion is the vertical travel. How was that measured? Very likely it was measured by the altimeter, which works by measuring the static port pressure. How do we know that the static port was measuring static pressure? Very likely it was not, because the turbulence would probably have had a lateral component, as indicated by the 20 degrees left and right rolls. Lateral wind (sideslip) means the static port is exposed to the airstream, and therefore measuring a mix of dynamic and static pressure. It could have been more than 500 ft, it could have been less. We simply don't know.
The most reliable way of determining g forces is by measuring them on-board and recording them (e.g. in the flight data recorder). With the data we have, there is simply no way to know what the g-force were.
In my opinion, it's very unlikely that the aircraft would have encountered 15 g.

The fact that an aircraft is certified for 2.5 g, doesn't mean it can't withstand more, as the crew of China Airlines flight 006 demonstrated on 19 February 1985. They managed to reach 5 g and bend the wing permanently 5 cm upwards. The aircraft was repaired and flew for another 20 years.

Note that the 2.5 g is for load due to manoeuvring, not only for turbulence. The certification specification for large aircraft on the subject of turbulence and gusts has changed several times since the certification of the DC-8.
In 1964, a formula was introduced describing the gust load that the structure aircraft has to deal with. This was added as FAR 25.341. This section has subsequently been updated in 1990, 1996 and 2015.

In addition to changes in structural requirements on the airframe, the origin of mountain wave turbulence in much better understood nowadays. It is taken into account in the operation of the flight.

If the DC-8 only felt 3G, why did part of the wing snap off? What about BOAC 911 which experienced +9 G and -4G?

@WillyA My remark about the 3g was an example to show that you can't conclude anything from the numbers given in the presentation. The claim in the title stating that 15 g was reached and that current certification only require 20% of that amount is based on false assumptions.

It's what they're certified to.  The DC-8 was also certified to 2.5 limit/3.75 ultimate but almost all airplanes are stronger than the minimum, and airplanes designed in the late 50s during the slide rule era are even stronger than that because of the need to apply much larger scatter factors in calculations, especially when you are taking fatigue life into account.  So the DC-8's structure would be expected to be a lot heavier than a more modern airplane designed using finite element analysis done by computer.
In airframe design, you have competing objectives - on the one hand every pound more than the minimum required is "ballast"; on the other, you have pad the numbers to allow for variability in many forms.  The last 50 years have seen computer design being used to shave more and more from the padding to get a lighter airframe that is still safe from the standpoint of a necessarily arbitrary risk profile.
Another is fatigue life.  A structure that sees a lot of flexing has to be stronger than the minimum required to take a single application of a load, so that it can take a lot of cycles of an intermediate load before cracks start to form.  Fatigue science was nowhere near as well developed in the 50s but it was known to be a problem, so it was accounted for with much larger structural margins than today. A good example is the DC-3, which being designed in the early 30s when the knowledge was very primitive, was made so robust that the fatigue life of the airframe is almost unlimited.
Also, a chunk of wing DID break off, that would have had the effect of partially unloading the rest of the structure.  That fact that the wing failed at that location instead of more inboard is probably what saved them.


text:
Can I get an EASA Class 1 medical if I have monocular vision?
I have monocular vision (amblyopia). In the USA I can get an FAA first class medical via a SODA waiver. Can I get an EASA Class 1 Medical issued with the same monocular problem? I would be applying for a medical in Ireland.
If I absolutely can’t get an EASA Class 1 medical, then will European airlines hire ATPs with a US FAA first class medical, or do EU airlines all require EASA Class 1 Medicals?

What country would you be looking to get an ATPL from? The EU is not a country with a single rule, each EASA member state has their own implementation, so your question cannot be answered as it is.

The CAA/EASA rules for visual acuity for class 1 and class 2 are here: https://www.caa.co.uk/Aeromedical-Examiners/Medical-standards/Pilots-(EASA)/Conditions/Visual/Visual-system-guidance-material-GM/  but they are confusing enough that I would not attempt to give you an interpretation. You should talk to an aviation medical examiner in Ireland for this.

The Irish Aviation Authority's aeromedical site directs you to the underlying EU regulations (Part-Med), which say:

Applicants for a Class 1 medical certificate shall be required to have
  normal fields of vision and normal binocular  function.

That seems to rule out monocular vision completely, which is very strange (to me) considering that the FAA is very clear that binocular vision isn't needed to fly safely. But medical issues are complicated, so I would definitely consult an aviation medical specialist in Ireland before making any decisions.
As for using an FAA medical certificate instead of an EASA one, that should really be a separate question. However, it's highly unlikely to be possible: generally speaking, your pilot's license/certificate and medical have to come from the same country.

I am European, and have amblyopia. Got an FAA First Class Medical without any issues.
SODA did not apply as AME decided it wasn't necessary and signed me off.
Have not had a reason to apply for a EASA medical, but I know pilots who have transferred without problems, and I am also aware of two pilots who have lost an eye and continue to fly with a Class 1 medical.
Good luck.

The answer to your question is... maybe! It really depends on the specifics of your situation, visual acuity wise etc. I'm also in your position. I have amblyopia and will be looking to take my initial EASA class 1 in the UK around May this year. I've researched this an awful lot and have had good success with vision therapy so far - no doubt you will have heard many doctors telling you it's too late to do anything. Not so!

@J.Hougaard I removed it. The point of this site is that the information answering the question should be here, for other people to find in the future, not hidden in people's private mails.


text:
What is the procedure to replace carpets in airliners?
Are all the seats removed, as well as trim and baseboard, before the carpet is replaced? If so, how is reinstalling the seats laid out; do they feel for the boltholes? Are the seats bolted on top of the carpet or directly to the floor?

Hobbes' answer seems to assume that you are asking about airliners. However, I don't think that's a given. Can you [Edit] to specify the kind of aircraft you're asking about?

I was asking about airliners, and Hobbes' answer was exactly what I was after. Thanks, Hobbes'.

Thanks for the clarification, Frank. I edited your question's title to clarify this. If you feel I got your intent wrong, by all means feel free to edit further.

If you feel that Hobbes' answer answers your question, you should indicate so by accepting it, by clicking the checkmark outline next to the voting buttons for the answer.

The seats are installed on rails, so they can be easily removed (or moved to a different seat pitch). The bolts are in plain sight (random source for example photo).

The carpets are laid around the rails. I suspect the carpet does not protrude underneath the base board, so they'd only have to remove the seats to get the carpet out.
This is the inside of an airliner with the seats and carpet removed:


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Pitot tube pressure question
I have this question is the pressure measured in the entry of the pitot tube the same  when the plane is flying headwind  or  turning a 360 degree turn while maintaining the same indicated airspeed?

Easiest thing is to imagine you're in a motorboat on a river, with a current, driving in circles at a constant water speed, indicated by a water speedometer that measures the dynamic pressure of the water more or less the same way as an airspeed.
Your path relative to the bottom of the river will be a spiral and your speed over the bottom will be faster or slower as you move with or against the current, as you make a perfect circle in the water, but your indicated speed through the water will be constant.
Airplanes are exactly the same.  The air is a big river.  You're just in it instead of floating on top.

Thanks for your explanation that's almost the same answer I gave to a friend of mine that's the one who is very hard to convince that it will be the same because the plane will be flying at the same indicated airspeed in any direction but he still says that there have to be a difference in the pressure at the entrance of the pitot tube due to the wind coming in a different direction but is hard to convince him and I ran out of explanation to try to make him understand, thanks for your answer

Airspeed is not affected due to wind because although wind direction changes the relative airflow aircraft is facing is always head-on. If it is not, it is called side slipping and pilots usually try to keep slipping as low possible because it adds drag and affects stability. In case of large side slip angles like in aerobatics the airspeed indicator will go haywire. Small side slip angles faced in everyday operations (including engine failures) have neglible effect.

Since the airspeed indicator measures pitot pressure, "same indicated airspeed" means same pitot pressure.